In one form or another, non-healing or chronic i.e. poorly healing wounds constitute a major burden on the UK health system. Moreover, in certain member countries of the EU health expenses relating to wound healing are already approaching the third most expensive drain on health care funding.
Chronic foot ulcers are a major complication of diabetes, accounting for up to 25% of all hospital admissions involving diabetes, and at a cost to the UK National Health Service of £250M annually. Chronic foot ulcers cause substantial morbidity, impair the quality of life, and are the major cause of lower limb amputation. Despite careful attention to foot care, as many as 25% of diabetics develop foot ulcers in their lifetimes. The causes of lower limb ulceration are the same in diabetics as in non-diabetics, namely neuropathy, ischaemia and trauma. Moreover, this “pathogenic triad” predisposes wounds to infection, which can also contribute to the non-healing nature of the wounds.
Current treatment involves removing pressure from the area, debridement, wound dressing and management of infection: surgical resection and vascular reconstruction may be required in more advanced disease which, ultimately, may necessitate amputation.
In addition to lower limb ulcers in diabetics, another major resource health cost is created by pressure wounds or ulcers that result, for example, from failure to provide routine nursing or medical care. In the UK 412,000 people are affected annually by this sort of wound at a cost of £1.4-2.1 billion.
The healing of a wound is controlled by complex biological processes that involve a diverse number of cell types; complex interactions between cells and tissues; the activation of the immune system and the activation of the angiogenic process.
A typical healing process can be divided into 5 distinct, but closely related, stages: clotting stage, acute inflammation stage, matrix deposition stage, capillary formation stage and re-epithelialisation stage. A diverse number of factors controls each of these stages. Deficiencies in any aspect of the process may result in defective wound healing. Thus, a ‘normal’ healing process may be defective as a result of either intrinsic or external factors, which manifest as ‘abnormal or non-healing’ i.e. chronic wounds. It is these ‘non-healing’ or chronic wounds that present the greatest challenge to the quality of a patient's life and mounting expenses to the healthcare system.
Although some common clinical/pathological factors may assist in pre judging if a wound may be ‘healing’ or ‘non-healing’, or if an acute wound may become chronic, there is no specific laboratory test(s) to distinguish wound type. Additionally, there is no clear way to define how to predict the healing process and a patient's likely response to treatment in wound care.
We have therefore developed a method for determining the prognosis of a given wound which is relatively straightforward to perform, efficient to undertake and provides an accurate indication of the likely outcome, before or during treatment, of a wound. Our method uses a small but highly representative sample of markers which distinguishes between acute wounds and chronic wounds and is therefore particularly relevant in the selection of treatment for a given wound and particularly accurate in determining the likely outcome, following treatment, of a given wound.
In summary, we have identified a plurality of molecular markers that have relevance in determining the prognosis of a given wound. Collectively these markers constitute at least one molecular signature and the expression of these markers in wound tissue from a patient constitutes a gene expression pattern that is indicative of a given wound type and prognosis. In addition to this, we have analysed the said molecular signature in order to identify which markers are the best indicators of wound type and prognosis, in other words those that contribute most to the predictive ability of the molecular signature. This subset of markers is known, collectively, as the refined molecular signature and the expression of these markers constitutes a refined gene expression pattern.
Reference herein to the term marker is reference to one named gene whose full identity is available on the www.NCBI.LM.NIH.gov database via its accession details, or is well known to those skilled in the art, please see Appendix-1. Moreover, a collection of these markers, or molecular signature, is to be construed accordingly.
The elucidation of the molecular signatures described herein has involved the systematic and careful examination of, in the first instance, 34 samples of wound tissue and 110 genetic molecular markers and, in the second instance, validation studies involving 71 samples of wound tissue and investigations to identify the use of the markers described herein.
However, having completed this arduous task we have, surprisingly, found that, in fact, very few genes need to be examined in order to provide an accurate classification and prognosis for a given sample of wound tissue. Even more surprisingly, we have been able to further reduce this number by identifying those molecular markers that contribute most to the predictive ability of our molecular signature, so for example, only 25 or, more ideally, 14 genes need to be examined. This means that our methodology has immediate application and can be performed quickly and routinely in a clinical context. In fact, we suggest that our methodology forms part of the standard treatment regime of wound care so that the relevant clinician can, at an early stage, determine the classification and outcome of a particular wound and so match the treatment accordingly. Thus, for example, in the case of an individual who presents with a signature indicative of an ‘abnormal’ or chronic wound a thorough and aggressive form of therapy might be prescribed. Conversely, if an individual has a signature indicative of a ‘normally healing’ or acute wound, the clinician can prescribe a less aggressive treatment, thereby saving the patient from any unnecessary distress and unwanted side effects and also saving the NHS from any costly and unnecessary, intervention. Our method therefore not only serves to ensure that individuals receive treatment tailored to their wound status, but it can improve the quality of a patient's life during treatment, by ensuring that aggressive therapy is only prescribed in those cases where it is necessary.